This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Based on our experience with the construction of homodyne 34 GHz spectrometer for Dr. Scholes upon his request, we proposed a future upgrade, based on our proprietary bridge design. This will considerably improve performance of pulse ENDOR based on this bridge. The existing version is an ad-on to his narrowband 34 GHz CW Bruker ER 200D spectrometer. The upgrade will convert it into a stand-alone instrument. The transmitter and receiver channels will be modified for the best performance. Peak power will be increased by a factor of 3 to 4W. The spectrometer will no longer require tunable ENDOR resonator, since the tuning bandwidths after upgrade will be at least 2 GHz. Also, digitizer unit will replace the boxcar averager, which is also a significant improvement for pulse ENDOR. This will enable complex frequency switching schemes, including pseudorandom mode.